The objectives of this project is to develop one or more in vivo mutagenesis assay systems to detect and quantitate gene mutations at a precisely defined target sequence in somatic, and possibly germ cells, of mice exposed to a test chemical. Such assays will provide a means to detect and analyze organ and tissue specific mutagenesis and study associations with chemical disposition, toxicity, and carcinogenicity. Ultimately, such systems may provide an in vivo short term assay with predictive value for carcinogenicity.